1. Field of the Invention
The present invention relates to devices for coupling electrical systems or devices together, and for balancing the impedances between the coupled systems or devices, and in particular to a blast hardened apparatus for matching the impedance of and producing a blast-hardened connection between two or more electrical elements.
2. The Prior Art
Circuits or devices for matching impedance in electrical systems are well known in the art. The importance of such impedance matching lies mainly in the fact that the matching of impedance allows optimum undistorted energy transfer between the connected electrical elements.
Devices for matching impedances often accomplish several purposes as part of their function, including: providing a physical connection between systems or devices; providing balanced impedance between those connected systems or devices; and, in some instances, providing shielding for the conductions and/or other protection for the systems by means of interconnected devices such as surge arresters.
One particular type of device which is often used for impedance matching is a balance to unbalance transformer (balun) which provides impedance matching in addition to balance-to-unbalance transformer coupling. Typically, a balun is a passive device having distributed electrical constants used to couple a balanced system or device to an unbalanced system or device, in addition to matching the impedances of the connected elements. The baluns generally comprise a ferrite core with multiple conductor windings positioned thereon.
The baluns and other devices and methods which are often utilized for impedance matching have generally been found to perform satisfactorily in conventional applications under normal operating conditions. However, such devices and methods have generally been considered "soft" for security purposes and have been unacceptable for applications involving operation under the force impact conditions for example due to explosion or natural disaster. "Hardness"(or "softness") is a military term used to denote the system's vulnerability to destruction. The harder a system is, the less vulnerable to destruction it is.
The hardness of an electrical system is often measured by such criteria as its ability to withstand substantial shock, as in the case of a powerful explosion occurring very near to the system, and its ability to survive high energy electromagnetic pulse radiation such as that which may be produced by a nuclear blast.
When devices for matching impedance are utilized in systems which are exposed to conditions such as those produced by nearby explosions, they are often exposed to extreme forces which have such destructive power that the devices may be destroyed or rendered unable to properly function. For example, when a balun having a ferrite core is exposed to a nearby, high powered blast, the resulting shock waves typically cause the core to shatter. Furthermore, if such systems are not provided with means for protecting them from voltage and/or current surges, exposure of the device and/or the systems to a nuclear explosion will likely disable the system since the electromagnetic pulse radiation produced by the explosion may induce an overload current in the conductors.
Conditions are even worse in situations where the device for matching impedances is utilized upon or beneath the surface of the earth. Particular applications that may require the impedance matching device to be positioned upon or beneath the surface of the earth include underground telephone or communication systems. These types of systems, of course, necessarily must be maintained in operating condition during times of natural disaster or enemy attack, when the probability of exposure to extreme forces is the highest. Particular embodiments of communication systems utilized upon or beneath the surface of the earth are described in the copending patent applications of Ferril A. Losee, U.S. Ser. Nos. 393,043 now allowed and 393,044 now allowed, each filed on June 23, 1982, and entitled, respectively, "Wireless Communication System Using Current Formed Underground Vertical Plane Polarized Antennas" and "Low Profile Wireless Communication System and Method", both of which are incorporated herein by reference.
The use of an impedance matching device is of particular importance in the communication systems described in the above-referenced applications. Specifically, in those systems, when the impedance of the earth and the current driver described therein are approximately matched (by means of an impedance matching device) to the impedance of a signal source, then ground currents are induced into the earth which, if correctly sized, define a loop of sufficient size to cause the earth and the current driver to essentially function together as a vertical plane polarized antenna. The absence of an impedance matching device would clearly hamper the ability to properly operate those systems.
Preferably, the impedance matching device in such systems is positioned, along with the systems elements, upon or beneath the surface of the earth. In such applications, the impedance matching device is necessarily subject to any movements or other actions of the surrounding earth. For example, when a large explosion occurs, it produces shock waves which travel throughout the surrounding environment including the air, earth and water. As the shock waves travel through the earth, they produce a substantial displacement of the ground, which responds in a manner similar to a fluid material. Thus, the earth is actually caused to rise and fall in a wave action, with the wave amplitude being from several inches to several feet, depending upon the size and location of the blast or other force which initiated the shock waves.
Baluns and similar devices which are often used for impedance matching purposes in conventional applications typically cannot withstand the extreme forces associated with the displacement of the earth by traveling shock waves, as described above. These devices typically secure the systems or devices to be interconnected by rigidly fastening the conductors associated with those systems that the conductors are tightly and securely held within the impedance matching device.
However, under the conditions associated with the traveling shock waves, the displacement of the earth often causes the securely fastened and rigidly held conductors to pull free or break. Thus, even though a powerful explosion may be centered some distance from the underground communication system, the resulting shock waves may likely result in breakage or separation of the conventional, tightly secured electrical connection. Of course, these types of ground conditions can also be associated with earthquakes and other similar natural phenomena, with the same, unacceptable results.
It is extremely important that communication systems such as those referenced above, as well as many other types of important electrical systems, be constructed so as to be able to withstand the excessive forces which may occur during natural disasters or as a result of enemy attack. Protection needs to be provided both to prevent the damaging effects resulting from the shock waves or displacement of the earth, and to prevent damage to electrical systems which may result from exposure to large amounts of electromagnetic pulse radiation produced by nuclear blasts.
It is under conditions such as these when the proper functioning of communication systems and similar important electronic equipment (which require impedance matching devices) is of utmost importance not only for local emergency purposes, but also to possibly preserve the national security. Nevertheless, a blast-hardened impedance matching device which provides the protection described above has not been made available and, thus, the problem continues to exist.
As is apparent from the above discussion, what is needed in the art is a blast-hardened device and method for matching the impedance of two or more systems or devices which are to be connected. A further improvement in the art would be to provide such an apparatus and method which additionally provides for blast-hardened connections between the systems and devices so that continuous electrical contact is maintained, even during the presence of extreme forces. Still a further improvement in the art would be to provide such a system which also includes a means for protecting the connected systems or devices from exposure to high amounts of electromagnetic pulse radiation. Yet another improvement in the art would be to provide such an apparatus and method which would include a means whereby a multiplicity of systems or devices could be electrically connected. Such an apparatus and method is disclosed and claimed herein.